Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 35-36


तत्र चन्द्रवसा नाम ताम्रपर्णी वटोदका ।तत्पुण्यसलिलैर्नित्यमुभयत्रात्मनो मृजन् ॥ ३५ ॥कन्दाष्टिभिर्मूलफलै: पुष्पपर्णैस्तृणोदकै: ।वर्तमान: शनैर्गात्रकर्शनं तप आस्थित: ॥ ३६ ॥


tatra candravasā nāmatāmraparṇī vaṭodakātat-puṇya-salilair nityamubhayatrātmano mṛjan


In the province of Kulācala, there were rivers named Candravasā, Tāmraparṇī and Vaṭodakā. King Malayadhvaja used to go to those pious rivers regularly and take his bath there. Thus he purified himself externally and internally. He took his bath and ate bulbs, seeds, leaves, flowers, roots, fruits and grasses and drank water. In this way he underwent severe austerities. Eventually he became very skinny.


We can definitely see that to advance in Kṛṣṇa consciousness one must control his bodily weight. If one becomes too fat, it is to be assumed that he is not advancing spiritually. Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura severely criticized his fat disciples. The idea is that one who intends to advance in Kṛṣṇa consciousness must not eat very much. Devotees used to go to forests, high hills or mountains on pilgrimages, but such severe austerities are not possible in these days. One should instead eat only prasāda and no more than required. According to the Vaiṣṇava calendar, there are many fasts, such as Ekādaśī and the appearance and disappearance days of God and His devotees. All of these are meant to decrease the fat within the body so that one will not sleep more than desired and will not become inactive and lazy. Overindulgence in food will cause a man to sleep more than required. This human form of life is meant for austerity, and austerity means controlling sex, food intake, etc. In this way time can be saved for spiritual activity, and one can purify himself both externally and internally. Thus both body and mind can be cleansed.